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    SubjectRe: [PATCH v4 1/1] Create debugfs file with virtio balloon usage information
    On Tue, Jul 05, 2022 at 08:36:37AM +0000, Alexander Atanasov wrote:
    > Allow the guest to know how much it is ballooned by the host.
    > It is useful when debugging out of memory conditions.
    >
    > When host gets back memory from the guest it is accounted
    > as used memory in the guest but the guest have no way to know
    > how much it is actually ballooned.
    >
    > Signed-off-by: Alexander Atanasov <alexander.atanasov@virtuozzo.com>
    > ---
    > drivers/virtio/virtio_balloon.c | 77 +++++++++++++++++++++++++++++
    > include/uapi/linux/virtio_balloon.h | 1 +
    > 2 files changed, 78 insertions(+)
    >
    > V2:
    > - fixed coding style
    > - removed pretty print
    > V3:
    > - removed dublicate of features
    > - comment about balooned_pages more clear
    > - convert host pages to balloon pages
    > V4:
    > - added a define for BALLOON_PAGE_SIZE to make things clear
    >
    > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
    > index b9737da6c4dd..dc4ad584b947 100644
    > --- a/drivers/virtio/virtio_balloon.c
    > +++ b/drivers/virtio/virtio_balloon.c
    > @@ -10,6 +10,7 @@
    > #include <linux/virtio_balloon.h>
    > #include <linux/swap.h>
    > #include <linux/workqueue.h>
    > +#include <linux/debugfs.h>
    > #include <linux/delay.h>
    > #include <linux/slab.h>
    > #include <linux/module.h>
    > @@ -731,6 +732,77 @@ static void report_free_page_func(struct work_struct *work)
    > }
    > }
    >
    > +/*
    > + * DEBUGFS Interface
    > + */
    > +#ifdef CONFIG_DEBUG_FS
    > +
    > +#define guest_to_balloon_pages(i) ((i)*VIRTIO_BALLOON_PAGES_PER_PAGE)
    > +/**
    > + * virtio_balloon_debug_show - shows statistics of balloon operations.
    > + * @f: pointer to the &struct seq_file.
    > + * @offset: ignored.
    > + *
    > + * Provides the statistics that can be accessed in virtio-balloon in the debugfs.
    > + *
    > + * Return: zero on success or an error code.
    > + */
    > +
    > +static int virtio_balloon_debug_show(struct seq_file *f, void *offset)
    > +{
    > + struct virtio_balloon *b = f->private;
    > + u32 num_pages;
    > + struct sysinfo i;
    > +
    > + si_meminfo(&i);
    > +
    > + seq_printf(f, "%-22s: %d\n", "page_size", VIRTIO_BALLOON_PAGE_SIZE);
    > +
    > + virtio_cread_le(b->vdev, struct virtio_balloon_config, actual,
    > + &num_pages);
    > + /*
    > + * Pages allocated by host from the guest memory.
    > + * Host inflates the balloon to get more memory.
    > + * Guest needs to deflate the balloon to get more memory.
    > + */
    > + seq_printf(f, "%-22s: %u\n", "ballooned_pages", num_pages);
    > +
    > + /* Total Memory for the guest from host */
    > + seq_printf(f, "%-22s: %lu\n", "total_pages",
    > + guest_to_balloon_pages(i.totalram));
    > +
    > + /* Current memory for the guest */
    > + seq_printf(f, "%-22s: %lu\n", "current_pages",
    > + guest_to_balloon_pages(i.totalram) - num_pages);
    > +
    > + return 0;
    > +}
    > +
    > +DEFINE_SHOW_ATTRIBUTE(virtio_balloon_debug);
    > +
    > +static void virtio_balloon_debugfs_init(struct virtio_balloon *b)
    > +{
    > + debugfs_create_file("virtio-balloon", 0444, NULL, b,
    > + &virtio_balloon_debug_fops);
    > +}
    > +
    > +static void virtio_balloon_debugfs_exit(struct virtio_balloon *b)
    > +{
    > + debugfs_remove(debugfs_lookup("virtio-balloon", NULL));
    > +}
    > +
    > +#else
    > +
    > +static inline void virtio_balloon_debugfs_init(struct virtio_balloon *b)
    > +{
    > +}
    > +
    > +static inline void virtio_balloon_debugfs_exit(struct virtio_balloon *b)
    > +{
    > +}
    > +
    > +#endif /* CONFIG_DEBUG_FS */
    > +
    > #ifdef CONFIG_BALLOON_COMPACTION
    > /*
    > * virtballoon_migratepage - perform the balloon page migration on behalf of
    > @@ -1019,6 +1091,9 @@ static int virtballoon_probe(struct virtio_device *vdev)
    >
    > if (towards_target(vb))
    > virtballoon_changed(vdev);
    > +
    > + virtio_balloon_debugfs_init(vb);
    > +
    > return 0;
    >
    > out_unregister_oom:
    > @@ -1065,6 +1140,8 @@ static void virtballoon_remove(struct virtio_device *vdev)
    > {
    > struct virtio_balloon *vb = vdev->priv;
    >
    > + virtio_balloon_debugfs_exit(vb);
    > +
    > if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING))
    > page_reporting_unregister(&vb->pr_dev_info);
    > if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
    > diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
    > index ddaa45e723c4..f3ff7c4e5884 100644
    > --- a/include/uapi/linux/virtio_balloon.h
    > +++ b/include/uapi/linux/virtio_balloon.h
    > @@ -40,6 +40,7 @@
    >
    > /* Size of a PFN in the balloon interface. */
    > #define VIRTIO_BALLOON_PFN_SHIFT 12
    > +#define VIRTIO_BALLOON_PAGE_SIZE (1<<VIRTIO_BALLOON_PFN_SHIFT)
    > #define VIRTIO_BALLOON_CMD_ID_STOP 0
    > #define VIRTIO_BALLOON_CMD_ID_DONE 1

    Did you run checkpatch on this?

    > --
    > 2.25.1

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